Saw-tooth current circuit



Sept. 17, 1940. HEPP SAW-TOOTH CURRENT CIRCUIT Filed June so, 1939 INVENTOR GERARD HEP/ ATTORNEYS Patented Sept. 17, 1940 PATENT OFFICE SAW-TOOTH CURRENT CIRCUIT Gerard Hepp, Eindhoven, Netherlands, assignor, by mesne assignments, to Radio Corporation of p America, New York, N. Y., a corporation of Delaware Application June 30, 1938, Serial No. 216,669 In the Netherlands August 25, 1937 4 Claims.

This invention relates to a circuit arrangement for supplying a saw-tooth current to a load-impedance, more particularly to the deflecting coils of a cathode ray tube that may be used in a television transmitter orreceiver. In order to obtain a saw-tooth current having a large amplitude it is customary to supply. the saw tooth current to the deflecting coils through a step-down transformer.

By means of the arrangement referred to above a uniform motion of the beam of cathode rays over the photosensitive or fluorescent screen in the cathode ray tube is obtained when the current traversing the deflecting coils varies linearly with the time or in other words when the voltage set up across the secondary winding of the transformer during that part of the period in which the current must be linear has a constant value. This result can be achieved by providing in parallel with the primary winding of the transformer the series-connection of a diode and a source of direct voltage, of which diode the cathode is connected to the high tension end of the transformer winding. However, the connection of the oathode of the diode to the high tension end of the primary transformer winding is a great drawback to this arrangement, since due to this an inadmissible high direct voltage is set up between the cathode of the diode andearth, in other words the filament.

The present invention has for its purpose to improve an arrangement of this kind in such a manner that this drawback is avoided.

According to the invention the transformer is equipped for this purpose with an additional winding with which the series-connection of a diode and a source of direct voltage is connected in parallel. The cathode of the diode may now be connected to earth, if desired. Another advantage of the arrangement according to the invention is that the tubular diode can be built in one of the other tubes of the arrangement.

The invention will be more clearly understood by reference to the accompanying drawing where- 5 in Figures 1 and 2 represent forms of construction of an arrangement according to the present invention, wherein only those parts are shown which are necessary for making the invention well understood.

The circuit arrangement represented in Figure 1 comprises a device I for producing a saw-tooth current which is supplied through a step-down transformer 2 to the deflecting coils 3 of a cathode ray tube 4. The transformer 2 comprises a 55 primary winding 5, a secondary winding 6 and an additional winding 1. In parallel with the additional winding 1 is provided the series-connection of a diode 8 and a source of direct voltage 9, the negative terminal of this supply being connected to the anode of the diode 8. The cathode of the diode 8 is connected to earth. The diode is so connected that during that part of the period, in which the course of the current through the deflecting coils must be linear, a positive Voltage is supplied to the anode of the diode by the voltage set up across the winding 1. Consequently the voltage at the anode of the diode 8 during the above-mentioned part of the period is determined by the difference between the voltage across the winding 1 and the voltage of the source of direct Voltage 9. The latter is so chosen that no current flows through the diode 8 when the voltage across the winding 1 has the desired constant value. If, however, the voltage across the winding 1 exceeds the desired value by some reason or other the diode 8 becomes conductive, whereby a further voltage increase across the winding 1 is rendered impossible. During the said period there will consequently be set up a constant voltage across the winding 1, due to which the voltage across the secondary winding is also constant and a purely saw-tooth current flows through the coils 3.

Figure 2 shows a form of construction in which the winding 1 is connected in series with the secondary winding 6. Furthermore the series-connection of the diode 8 and a source of direct voltage is connected in parallel with the series-connection of the secondary winding 6 and the winding 1. In this figure the voltage supply is constituted by the parallel-connection of a resistance I0 and a condenser II across which resistance the current traversing the diode 8 causes a direct voltage whose direction is opposite to that of the voltage set up across the winding 1 during the period part referred to. The operation of this arrangement exactly corresponds to that shown in Figure 1.

I claim:

1. A system for producing oscillations of sawtooth wave form comprising means for generating a current variation of saw-tooth wave form, means for applying the generated wave form to the primary winding of a transformer at a potential greater than a predetermined minimum, a pair of secondary windings, means for connecting a load impedance to one of said secondary windings, and means for connecting a rectifier and a source of potential in series and to the other of said secondary windings, the source of potential being connected to oppose the flow of current through said rectifier whereby the rate of change in the saw-tooth wave form will remain constant.

2. A system for producing oscillations of sawtooth wave form comprising means for generating a current variation of saw-tooth wave form, a transformer having a primary anda pair of secondary windings, means for applying the generated wave form to the primary Winding of said transformer at a potential greater than a predetermined minimum, means for connecting a load impedance to one of the secondary windings, and a unidirectional current path and a source of current connected in series and connected to the other secondary winding, said source of current being connected to oppose the flow of current through the unidirectional current path whereby linearity in the rate of change of the current wave will be assured.

3. A system for producing oscillations of sawtooth wave form comprising means for generating a current variation of saw-tooth Wave form, a transformer having a primary and a secondary Winding, means for applying the generated Wave form to the primary of said transformer at a potential greater than a predetermined minimum, an asymmetric unit and a source of potential connected in series and connected to the secondary winding of said transformer, and a load impedance connected across at least a portion of said secondary, the source of'potential being connected to oppose the flow of current through the asymmetric unit whereby a true saw-tooth wave form of constant rate of current change will be produced.

4. A system for producing oscillations of 'sawtooth wave form comprising means for generating current variations of substantially saw-tooth wave form, a transformer having mutually inductive primary and secondary means, means for applying the generated wave form to the primary inductive means at a potential greater than a predetermined minimum, means for connecting a load impedance across a portion of the secondary inductive means, and a uni-directional current path and a source of potential connected in series and connected across at least a portion of the secondary inductive means, said source of potential being connected to oppose the flow of current through the unidirectional current path whereby linearity in the rate of change of the current Wave will be assured.

GERARD HEPR' 

